不定代词被当作名词一样用是实际存在的现象。像这种非正式语体的小众用法，词典估计不大可能会有专门介绍，语法也未必会提及。但在一般文体中，特别是口语和文学体裁中并不罕见。以someone为例：

 Laura had telephoned every library in Burlington, Iowa, got someone who knew someone, got a someone who knew the married name and phone number of the subject of our search.（American Heritage: Dec94: Vol. 45 Issue 8, p110）

 In another few seconds, they had grasped a rope of twisted gold that an unseen someone lowered from above. They wrapped their legs around it and around each other. （Nights in black satin ）

 So I'll look into ways that you can de-cloak an invisible someone. What about you? Cordelia might be working on her dress tonight. Maybe there'll be some action. I guess I'm gonna start the hunt. How exactly do you propose to hunt someone you can't see? （Movie：Buffy the Vampire Slayer）

In profile, he is talking to an invisible someone. (Fiction: Set This House on Fire)

I asked a certain someone, who made me promise not to name her by the way, to do me a favour. （Fiction：New year - new luck）

Um... go out on a date with a special someone or with a new crush. (US movie：100 Yards)

此时的someone并非词典中所介绍的an important person之意，基本意思仍相当于someone的原意“某人，某个人”。例如：an invisible someone=someone special，an invisible someone=someone invisible，a certain someone = someone 等等。只是表达的手法有所改变，可能具有更加“未知”、更为生动和强烈的效果。

something也可这样用。例如：

In the fluid in which it multiplied was a something that killed several kinds of microbes.（TIME）

其中的a something如果直接改为something，在读者的感觉中这一物质的神秘感就会被打折扣。

此外，人称代词也可用作名词。例如：

What a darling puppy! Is it a he or a she? 

  To save her life, Dr. Mengers rebuilt and re-endowed her as Myron Breckinridge: the man, in fact, who Myra had originally been before a sex-change operation transformed him into  a her. （TIME）

    供参考。